On Monday, May 22, 2017 at 1:43:21 PM UTC-7, Joerg wrote:
The BB on my steel-frame bike is knackered and I can't get the cranks
off the square tapers anymore. Afraid I'll strip out the thread of the
puller tool. Various penetrating sprays didn't help.

From the last time the BB was replaced the bike experienced a transport
across the Atlantic on a ship which probably hasn't helped matters.

Any tricks of the trade?

--
Regards, Joerg

http://www.analogconsultants.com/

Yee gods. Try heating the crank up with a propane torch not so hot that you can't touch it. Avoid heating the steel BB shaft. Spray your penetrating oil on it and let it cool and then try again.